1. Field of the Invention
The present invention relates generally to methods of forming mechanical joints between lengths of pipe and more particularly to pipe of the type and quality typically utilized in oil field applications, such as gathering lines for distribution systems down-hole casing, and the like, and to the joints so formed. It is particularly adapted for joining materials heretofore considered highly difficult if not impossible to join mechanically with consistent reliability, namely, plain aluminum pipe and steel pipe.
2. Description of the Prior Art
The literature contains many schemes for mechanically joining pipes, tubing and the like, only a few of which have proved actually capable of forming leak-free joints with oil-field materials. One such method known to be actually operative is that disclosed in U.S. Pat. No. 3,208,136. Such patent discloses a pipe-joining method consisting essentially of forming a bell on one pipe end, rolling an annular groove in another pipe end, and telescoping the latter into the former. Additionally, one or the other of the two surfaces was typically coated with a liquid lubricant-sealant prior to the joining of the pipes. Related U.S. Pat. No. 3,210,102 discloses the coupling or joint essentially formed by the above-described method.
U.S. Pat. No. 3,466,738 discloses a method of joining pipe consisting essentially of simply forcing together two pipe ends of like diameter, the only preparatory step being the slight flaring of one tip in order to permit the initial entry of the other. The amount of force and the time required to so join two such pipe ends is many times greater than that required by the method of the present invention, and it is likely that galling of the parts can occur.